I don't understand your question. At all.

If you want to find out your SIP credentials, the link is on the localphone help page, linked above. Your original problem is that you have not defined routing of localphone incoming calls. The default context, one that you posted, does not go anywhere. Don't change the default context. It should be left as you have it, to minimize the chances of abuse. Define another context, localphone-in, you can name it anything you like really, and make sure that all the calls that reach that context get routed to your local user (1001 in your original example).

You do have a localphone incoming number (DID), don't you?

Why do you want to use asterisk in the first place? Don't setup an asterisk server if you are not fully aware of all the security considerations! You definitely don't need it to connect N900 with (most) VOIP service providers.

-m